1 (** Bitstring library. *)
2 (* Copyright (C) 2008 Red Hat Inc., Richard W.M. Jones
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version,
8 * with the OCaml linking exception described in COPYING.LIB.
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with this library; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 {{:#reference}Jump straight to the reference section for
24 documentation on types and functions}.
28 Bitstring adds Erlang-style bitstrings and matching over bitstrings
29 as a syntax extension and library for OCaml. You can use
30 this module to both parse and generate binary formats, for
31 example, communications protocols, disk formats and binary files.
33 {{:http://code.google.com/p/bitstring/}OCaml bitstring website}
35 This library used to be called "bitmatch".
39 A function which can parse IPv4 packets:
46 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
47 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
48 | 4 | IHL |Type of Service| Total Length |
49 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
50 | Identification |Flags| Fragment Offset |
51 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
52 | Time to Live | Protocol | Header Checksum |
53 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
55 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
56 | Destination Address |
57 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
59 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
61 | { 4 : 4; hdrlen : 4; tos : 8; length : 16;
62 identification : 16; flags : 3; fragoffset : 13;
63 ttl : 8; protocol : 8; checksum : 16;
66 options : (hdrlen-5)*32 : bitstring;
67 payload : -1 : bitstring } ->
70 printf " header length: %d * 32 bit words\n" hdrlen;
71 printf " type of service: %d\n" tos;
72 printf " packet length: %d bytes\n" length;
73 printf " identification: %d\n" identification;
74 printf " flags: %d\n" flags;
75 printf " fragment offset: %d\n" fragoffset;
76 printf " ttl: %d\n" ttl;
77 printf " protocol: %d\n" protocol;
78 printf " checksum: %d\n" checksum;
79 printf " source: %lx dest: %lx\n" source dest;
80 printf " header options + padding:\n";
81 Bitstring.hexdump_bitstring stdout options;
82 printf " packet payload:\n";
83 Bitstring.hexdump_bitstring stdout payload
86 eprintf "unknown IP version %d\n" version;
90 eprintf "data is smaller than one nibble:\n";
91 Bitstring.hexdump_bitstring stderr pkt;
95 A program which can parse
96 {{:http://lxr.linux.no/linux/include/linux/ext3_fs.h}Linux EXT3 filesystem superblocks}:
99 let bits = Bitstring.bitstring_of_file "tests/ext3_sb"
103 | { s_inodes_count : 32 : littleendian; (* Inodes count *)
104 s_blocks_count : 32 : littleendian; (* Blocks count *)
105 s_r_blocks_count : 32 : littleendian; (* Reserved blocks count *)
106 s_free_blocks_count : 32 : littleendian; (* Free blocks count *)
107 s_free_inodes_count : 32 : littleendian; (* Free inodes count *)
108 s_first_data_block : 32 : littleendian; (* First Data Block *)
109 s_log_block_size : 32 : littleendian; (* Block size *)
110 s_log_frag_size : 32 : littleendian; (* Fragment size *)
111 s_blocks_per_group : 32 : littleendian; (* # Blocks per group *)
112 s_frags_per_group : 32 : littleendian; (* # Fragments per group *)
113 s_inodes_per_group : 32 : littleendian; (* # Inodes per group *)
114 s_mtime : 32 : littleendian; (* Mount time *)
115 s_wtime : 32 : littleendian; (* Write time *)
116 s_mnt_count : 16 : littleendian; (* Mount count *)
117 s_max_mnt_count : 16 : littleendian; (* Maximal mount count *)
118 0xef53 : 16 : littleendian } -> (* Magic signature *)
120 printf "ext3 superblock:\n";
121 printf " s_inodes_count = %ld\n" s_inodes_count;
122 printf " s_blocks_count = %ld\n" s_blocks_count;
123 printf " s_free_inodes_count = %ld\n" s_free_inodes_count;
124 printf " s_free_blocks_count = %ld\n" s_free_blocks_count
127 eprintf "not an ext3 superblock!\n%!";
131 Constructing packets for a simple binary message
136 +---------------+---------------+--------------------------+
137 | type | subtype | parameter |
138 +---------------+---------------+--------------------------+
139 <-- 16 bits --> <-- 16 bits --> <------- 32 bits -------->
141 All fields are in network byte order.
144 let make_message typ subtype param =
152 {2 Loading, creating bitstrings}
154 The basic data type is the {!bitstring}, a string of bits of
155 arbitrary length. Bitstrings can be any length in bits and
156 operations do not need to be byte-aligned (although they will
157 generally be more efficient if they are byte-aligned).
159 Internally a bitstring is stored as a normal OCaml [string]
160 together with an offset and length, where the offset and length are
161 measured in bits. Thus one can efficiently form substrings of
162 bitstrings, overlay a bitstring on existing data, and load and save
163 bitstrings from files or other external sources.
165 To load a bitstring from a file use {!bitstring_of_file} or
166 {!bitstring_of_chan}.
168 There are also functions to create bitstrings from arbitrary data.
169 See the {{:#reference}reference} below.
171 {2 Matching bitstrings with patterns}
173 Use the [bitmatch] operator (part of the syntax extension) to break
174 apart a bitstring into its fields. [bitmatch] works a lot like the
175 OCaml [match] operator.
177 The general form of [bitmatch] is:
179 [bitmatch] {i bitstring-expression} [with]
181 [| {] {i pattern} [} ->] {i code}
183 [| {] {i pattern} [} ->] {i code}
187 As with normal match, the statement attempts to match the
188 bitstring against each pattern in turn. If none of the patterns
189 match then the standard library [Match_failure] exception is
192 Patterns look a bit different from normal match patterns. They
193 consist of a list of bitfields separated by [;] where each bitfield
194 contains a bind variable, the width (in bits) of the field, and
195 other information. Some example patterns:
200 | { version : 8; name : 8; param : 8 } -> ...
202 (* Bitstring of at least 3 bytes. First byte is the version
203 number, second byte is a field called name, third byte is
204 a field called parameter. *)
207 printf "flag is %b\n" flag
209 (* A single flag bit (mapped into an OCaml boolean). *)
211 | { len : 4; data : 1+len } ->
212 printf "len = %d, data = 0x%Lx\n" len data
214 (* A 4-bit length, followed by 1-16 bits of data, where the
215 length of the data is computed from len. *)
217 | { ipv6_source : 128 : bitstring;
218 ipv6_dest : 128 : bitstring } -> ...
220 (* IPv6 source and destination addresses. Each is 128 bits
221 and is mapped into a bitstring type which will be a substring
222 of the main bitstring expression. *)
225 You can also add conditional when-clauses:
229 when version = 4 || version = 6 -> ...
231 (* Only match and run the code when version is 4 or 6. If
232 it isn't we will drop through to the next case. *)
235 Note that the pattern is only compared against the first part of
236 the bitstring (there may be more data in the bitstring following
237 the pattern, which is not matched). In terms of regular
238 expressions you might say that the pattern matches [^pattern], not
239 [^pattern$]. To ensure that the bitstring contains only the
240 pattern, add a length -1 bitstring to the end and test that its
241 length is zero in the when-clause:
245 rest : -1 : bitstring }
246 when Bitstring.bitstring_length rest = 0 -> ...
248 (* Only matches exactly 4 bits. *)
251 Normally the first part of each field is a binding variable,
252 but you can also match a constant, as in:
255 | { (4|6) : 4 } -> ...
257 (* Only matches if the first 4 bits contain either
258 the integer 4 or the integer 6. *)
261 One may also match on strings:
264 | { "MAGIC" : 5*8 : string } -> ...
266 (* Only matches if the string "MAGIC" appears at the start
270 {3:patternfieldreference Pattern field reference}
272 The exact format of each pattern field is:
274 [pattern : length [: qualifier [,qualifier ...]]]
276 [pattern] is the pattern, binding variable name, or constant to
277 match. [length] is the length in bits which may be either a
278 constant or an expression. The length expression is just an OCaml
279 expression and can use any values defined in the program, and refer
280 back to earlier fields (but not to later fields).
282 Integers can only have lengths in the range \[1..64\] bits. See the
283 {{:#integertypes}integer types} section below for how these are
284 mapped to the OCaml int/int32/int64 types. This is checked
285 at compile time if the length expression is constant, otherwise it is
286 checked at runtime and you will get a runtime exception eg. in
287 the case of a computed length expression.
289 A bitstring field of length -1 matches all the rest of the
290 bitstring (thus this is only useful as the last field in a
293 A bitstring field of length 0 matches an empty bitstring
294 (occasionally useful when matching optional subfields).
296 Qualifiers are a list of identifiers/expressions which control the type,
297 signedness and endianness of the field. Permissible qualifiers are:
299 - [int]: field has an integer type
300 - [string]: field is a string type
301 - [bitstring]: field is a bitstring type
302 - [signed]: field is signed
303 - [unsigned]: field is unsigned
304 - [bigendian]: field is big endian - a.k.a network byte order
305 - [littleendian]: field is little endian - a.k.a Intel byte order
306 - [nativeendian]: field is same endianness as the machine
307 - [endian (expr)]: [expr] should be an expression which evaluates to
308 a {!endian} type, ie. [LittleEndian], [BigEndian] or [NativeEndian].
309 The expression is an arbitrary OCaml expression and can use the
310 value of earlier fields in the bitmatch.
311 - [offset (expr)]: see {{:#computedoffsets}computed offsets} below.
313 The default settings are [int], [unsigned], [bigendian], no offset.
315 Note that many of these qualifiers cannot be used together,
316 eg. bitstrings do not have endianness. The syntax extension should
317 give you a compile-time error if you use incompatible qualifiers.
319 {3 Other cases in bitmatch}
321 As well as a list of fields, it is possible to name the
322 bitstring and/or have a default match case:
327 (* Default match case. *)
329 | { _ } as pkt -> ...
331 (* Default match case, with 'pkt' bound to the whole bitstring. *)
334 {2 Constructing bitstrings}
336 Bitstrings may be constructed using the [BITSTRING] operator (as an
337 expression). The [BITSTRING] operator takes a list of fields,
338 similar to the list of fields for matching:
349 (* Constructs a 16-bit bitstring with the first four bits containing
350 the integer 1, and the following 12 bits containing the integer 10,
351 arranged in network byte order. *)
353 Bitstring.hexdump_bitstring stdout bits ;;
361 The format of each field is the same as for pattern fields (see
362 {{:#patternfieldreference}Pattern field reference section}), and
363 things like computed length fields, fixed value fields, insertion
364 of bitstrings within bitstrings, etc. are all supported.
366 {3 Construction exception}
368 The [BITSTRING] operator may throw a {!Construct_failure}
369 exception at runtime.
371 Runtime errors include:
373 - int field length not in the range \[1..64\]
374 - a bitstring with a length declared which doesn't have the
375 same length at runtime
376 - trying to insert an out of range value into an int field
377 (eg. an unsigned int field which is 2 bits wide can only
378 take values in the range \[0..3\]).
380 {2:integertypes Integer types}
382 Integer types are mapped to OCaml types [bool], [int], [int32] or
383 [int64] using a system which tries to ensure that (a) the types are
384 reasonably predictable and (b) the most efficient type is
387 The rules are slightly different depending on whether the bit
388 length expression in the field is a compile-time constant or a
391 Detection of compile-time constants is quite simplistic so only
392 simple integer literals and simple expressions (eg. [5*8]) are
393 recognized as constants.
395 In any case the bit size of an integer is limited to the range
396 \[1..64\]. This is detected as a compile-time error if that is
397 possible, otherwise a runtime check is added which can throw an
398 [Invalid_argument] exception.
403 Bit size ---- OCaml type ----
404 Constant Computed expression
412 A possible future extension may allow people with 64 bit computers
413 to specify a more optimal [int] type for bit sizes in the range
414 [32..63]. If this was implemented then such code {i could not even
415 be compiled} on 32 bit platforms, so it would limit portability.
417 Another future extension may be to allow computed
418 expressions to assert min/max range for the bit size,
419 allowing a more efficient data type than int64 to be
420 used. (Of course under such circumstances there would
421 still need to be a runtime check to enforce the
424 {2 Advanced pattern-matching features}
426 {3:computedoffsets Computed offsets}
428 You can add an [offset(..)] qualifier to bitmatch patterns in order
429 to move the current offset within the bitstring forwards.
436 field2 : 8 : offset(160) } -> ...
439 matches [field1] at the start of the bitstring and [field2]
440 at 160 bits into the bitstring. The middle 152 bits go
441 unmatched (ie. can be anything).
443 The generated code is efficient. If field lengths and offsets
444 are known to be constant at compile time, then almost all
445 runtime checks are avoided. Non-constant field lengths and/or
446 non-constant offsets can result in more runtime checks being added.
448 Note that moving the offset backwards, and moving the offset in
449 [BITSTRING] constructors, are both not supported at present.
451 {3 Check expressions}
453 You can add a [check(expr)] qualifier to bitmatch patterns.
454 If the expression evaluates to false then the current match case
455 fails to match (in other words, we fall through to the next
456 match case - there is no error).
461 | { field : 16 : check (field > 100) } -> ...
464 Note the difference between a check expression and a when-clause
465 is that the when-clause is evaluated after all the fields have
466 been matched. On the other hand a check expression is evaluated
467 after the individual field has been matched, which means it is
468 potentially more efficient (if the check expression fails then
469 we don't waste any time matching later fields).
471 We wanted to use the notation [when(expr)] here, but because
472 [when] is a reserved word we could not do this.
476 A bind expression is used to change the value of a matched
480 | { len : 16 : bind (len * 8);
481 field : len : bitstring } -> ...
484 In the example, after 'len' has been matched, its value would
485 be multiplied by 8, so the width of 'field' is the matched
486 value multiplied by 8.
490 | { field : ... : bind (expr) } -> ...
492 evaluates the following after the field has been matched:
495 (* remaining fields *)
498 {3 Order of evaluation of check() and bind()}
500 The choice is arbitrary, but we have chosen that check expressions
501 are evaluated first, and bind expressions are evaluated after.
503 This means that the result of bind() is {i not} available in
504 the check expression.
506 Note that this rule applies regardless of the order of check()
507 and bind() in the source code.
511 Use [save_offset_to(variable)] to save the current bit offset
512 within the match to a variable (strictly speaking, to a pattern).
513 This variable is then made available in any [check()] and [bind()]
514 clauses in the current field, {i and} to any later fields, and
515 to the code after the [->].
522 field : 16 : save_offset_to (field_offset) } ->
523 printf "field is at bit offset %d in the match\n" field_offset
526 (In that example, [field_offset] should always have the value
529 {2 Named patterns and persistent patterns}
531 Please see {!Bitstring_persistent} for documentation on this subject.
535 Using the compiler directly you can do:
538 ocamlc -I +bitstring \
539 -pp "camlp4of bitstring.cma bitstring_persistent.cma \
540 `ocamlc -where`/bitstring/pa_bitstring.cmo" \
541 unix.cma bitstring.cma test.ml -o test
544 Simpler method using findlib:
548 -package bitstring,bitstring.syntax -syntax bitstring.syntax \
549 -linkpkg test.ml -o test
552 {2 Security and type safety}
554 {3 Security on input}
556 The main concerns for input are buffer overflows and denial
559 It is believed that this library is robust against attempted buffer
560 overflows. In addition to OCaml's normal bounds checks, we check
561 that field lengths are >= 0, and many additional checks.
563 Denial of service attacks are more problematic. We only work
564 forwards through the bitstring, thus computation will eventually
565 terminate. As for computed lengths, code such as this is thought
571 buffer : Int64.to_int len : bitstring } ->
574 The [len] field can be set arbitrarily large by an attacker, but
575 when pattern-matching against the [buffer] field this merely causes
576 a test such as [if len <= remaining_size] to fail. Even if the
577 length is chosen so that [buffer] bitstring is allocated, the
578 allocation of sub-bitstrings is efficient and doesn't involve an
579 arbitary-sized allocation or any copying.
581 However the above does not necessarily apply to strings used in
582 matching, since they may cause the library to use the
583 {!Bitstring.string_of_bitstring} function, which allocates a string.
584 So you should take care if you use the [string] type particularly
585 with a computed length that is derived from external input.
587 The main protection against attackers should be to ensure that the
588 main program will only read input bitstrings up to a certain
589 length, which is outside the scope of this library.
591 {3 Security on output}
593 As with the input side, computed lengths are believed to be
597 let len = read_untrusted_source () in
598 let buffer = allocate_bitstring () in
600 buffer : len : bitstring
604 This code merely causes a check that buffer's length is the same as
605 [len]. However the program function [allocate_bitstring] must
606 refuse to allocate an oversized buffer (but that is outside the
607 scope of this library).
609 {3 Order of evaluation}
611 In [bitmatch] statements, fields are evaluated left to right.
613 Note that the when-clause is evaluated {i last}, so if you are
614 relying on the when-clause to filter cases then your code may do a
615 lot of extra and unncessary pattern-matching work on fields which
616 may never be needed just to evaluate the when-clause. Either
617 rearrange the code to do only the first part of the match,
618 followed by the when-clause, followed by a second inner bitmatch,
619 or use a [check()] qualifier within fields.
623 The current implementation is believed to be fully type-safe,
624 and makes compile and run-time checks where appropriate. If
625 you find a case where a check is missing please submit a
626 bug report or a patch.
630 These are thought to be the current limits:
632 Integers: \[1..64\] bits.
634 Bitstrings (32 bit platforms): maximum length is limited
635 by the string size, ie. 16 MBytes.
637 Bitstrings (64 bit platforms): maximum length is thought to be
638 limited by the string size, ie. effectively unlimited.
640 Bitstrings must be loaded into memory before we can match against
641 them. Thus available memory may be considered a limit for some
644 {2:reference Reference}
648 type endian = BigEndian | LittleEndian | NativeEndian
650 val string_of_endian : endian -> string
653 type bitstring = string * int * int
654 (** [bitstring] is the basic type used to store bitstrings.
656 The type contains the underlying data (a string),
657 the current bit offset within the string and the
658 current bit length of the string (counting from the
659 bit offset). Note that the offset and length are
660 in {b bits}, not bytes.
662 Normally you don't need to use the bitstring type
663 directly, since there are functions and syntax
664 extensions which hide the details.
666 See also {!bitstring_of_string}, {!bitstring_of_file},
667 {!hexdump_bitstring}, {!bitstring_length}.
671 (** [t] is a synonym for the {!bitstring} type.
673 This allows you to use this module with functors like
674 [Set] and [Map] from the stdlib. *)
676 (** {3 Exceptions} *)
678 exception Construct_failure of string * string * int * int
679 (** [Construct_failure (message, file, line, char)] may be
680 raised by the [BITSTRING] constructor.
682 Common reasons are that values are out of range of
683 the fields that contain them, or that computed lengths
684 are impossible (eg. negative length bitfields).
686 [message] is the error message.
688 [file], [line] and [char] point to the original source
689 location of the [BITSTRING] constructor that failed.
692 (** {3 Bitstring comparison} *)
694 val compare : bitstring -> bitstring -> int
695 (** [compare bs1 bs2] compares two bitstrings and returns zero
696 if they are equal, a negative number if [bs1 < bs2], or a
697 positive number if [bs1 > bs2].
699 This tests "semantic equality" which is not affected by
700 the offset or alignment of the underlying representation
703 The ordering is total and lexicographic. *)
705 val equals : bitstring -> bitstring -> bool
706 (** [equals] returns true if and only if the two bitstrings are
707 semantically equal. It is the same as calling [compare] and
708 testing if the result is [0], but usually more efficient. *)
710 val is_zeroes_bitstring : bitstring -> bool
711 (** Tests if the bitstring is all zero bits (cf. {!zeroes_bitstring}) *)
713 val is_ones_bitstring : bitstring -> bool
714 (** Tests if the bitstring is all one bits (cf. {!ones_bitstring}). *)
716 (** {3 Bitstring manipulation} *)
718 val bitstring_length : bitstring -> int
719 (** [bitstring_length bitstring] returns the length of
720 the bitstring in bits.
722 Note this just returns the third field in the {!bitstring} tuple. *)
724 val subbitstring : bitstring -> int -> int -> bitstring
725 (** [subbitstring bits off len] returns a sub-bitstring
726 of the bitstring, starting at offset [off] bits and
727 with length [len] bits.
729 If the original bitstring is not long enough to do this
730 then the function raises [Invalid_argument "subbitstring"].
732 Note that this function just changes the offset and length
733 fields of the {!bitstring} tuple, so is very efficient. *)
735 val dropbits : int -> bitstring -> bitstring
736 (** Drop the first n bits of the bitstring and return a new
737 bitstring which is shorter by n bits.
739 If the length of the original bitstring is less than n bits,
740 this raises [Invalid_argument "dropbits"].
742 Note that this function just changes the offset and length
743 fields of the {!bitstring} tuple, so is very efficient. *)
745 val takebits : int -> bitstring -> bitstring
746 (** Take the first n bits of the bitstring and return a new
747 bitstring which is exactly n bits long.
749 If the length of the original bitstring is less than n bits,
750 this raises [Invalid_argument "takebits"].
752 Note that this function just changes the offset and length
753 fields of the {!bitstring} tuple, so is very efficient. *)
755 val concat : bitstring list -> bitstring
756 (** Concatenate a list of bitstrings together into a single
759 (** {3 Constructing bitstrings} *)
761 val empty_bitstring : bitstring
762 (** [empty_bitstring] is the empty, zero-length bitstring. *)
764 val create_bitstring : int -> bitstring
765 (** [create_bitstring n] creates an [n] bit bitstring
766 containing all zeroes. *)
768 val make_bitstring : int -> char -> bitstring
769 (** [make_bitstring n c] creates an [n] bit bitstring
770 containing the repeated 8 bit pattern in [c].
772 For example, [make_bitstring 16 '\x5a'] will create
773 the bitstring [0x5a5a] or in binary [0101 1010 0101 1010].
775 Note that the length is in bits, not bytes. The length does NOT
776 need to be a multiple of 8. *)
778 val zeroes_bitstring : int -> bitstring
779 (** [zeroes_bitstring] creates an [n] bit bitstring of all 0's.
781 Actually this is the same as {!create_bitstring}. *)
783 val ones_bitstring : int -> bitstring
784 (** [ones_bitstring] creates an [n] bit bitstring of all 1's. *)
786 val bitstring_of_string : string -> bitstring
787 (** [bitstring_of_string str] creates a bitstring
788 of length [String.length str * 8] (bits) containing the
791 Note that the bitstring uses [str] as the underlying
792 string (see the representation of {!bitstring}) so you
793 should not change [str] after calling this. *)
795 val bitstring_of_file : string -> bitstring
796 (** [bitstring_of_file filename] loads the named file
799 val bitstring_of_chan : in_channel -> bitstring
800 (** [bitstring_of_chan chan] loads the contents of
801 the input channel [chan] as a bitstring.
803 The length of the final bitstring is determined
804 by the remaining input in [chan], but will always
805 be a multiple of 8 bits.
807 See also {!bitstring_of_chan_max}. *)
809 val bitstring_of_chan_max : in_channel -> int -> bitstring
810 (** [bitstring_of_chan_max chan max] works like
811 {!bitstring_of_chan} but will only read up to
812 [max] bytes from the channel (or fewer if the end of input
813 occurs before that). *)
815 val bitstring_of_file_descr : Unix.file_descr -> bitstring
816 (** [bitstring_of_file_descr fd] loads the contents of
817 the file descriptor [fd] as a bitstring.
819 See also {!bitstring_of_chan}, {!bitstring_of_file_descr_max}. *)
821 val bitstring_of_file_descr_max : Unix.file_descr -> int -> bitstring
822 (** [bitstring_of_file_descr_max fd max] works like
823 {!bitstring_of_file_descr} but will only read up to
824 [max] bytes from the channel (or fewer if the end of input
825 occurs before that). *)
827 (** {3 Converting bitstrings} *)
829 val string_of_bitstring : bitstring -> string
830 (** [string_of_bitstring bitstring] converts a bitstring to a string
831 (eg. to allow comparison).
833 This function is inefficient. In the best case when the bitstring
834 is nicely byte-aligned we do a [String.sub] operation. If the
835 bitstring isn't aligned then this involves a lot of bit twiddling
836 and is particularly inefficient.
838 If the bitstring is not a multiple of 8 bits wide then the
839 final byte of the string contains the high bits set to the
840 remaining bits and the low bits set to 0. *)
842 val bitstring_to_file : bitstring -> string -> unit
843 (** [bitstring_to_file bits filename] writes the bitstring [bits]
844 to the file [filename]. It overwrites the output file.
846 Some restrictions apply, see {!bitstring_to_chan}. *)
848 val bitstring_to_chan : bitstring -> out_channel -> unit
849 (** [bitstring_to_file bits filename] writes the bitstring [bits]
850 to the channel [chan].
852 Channels are made up of bytes, bitstrings can be any bit length
853 including fractions of bytes. So this function only works
854 if the length of the bitstring is an exact multiple of 8 bits
855 (otherwise it raises [Invalid_argument "bitstring_to_chan"]).
857 Furthermore the function is efficient only in the case where
858 the bitstring is stored fully aligned, otherwise it has to
859 do inefficient bit twiddling like {!string_of_bitstring}.
861 In the common case where the bitstring was generated by the
862 [BITSTRING] operator and is an exact multiple of 8 bits wide,
863 then this function will always work efficiently.
866 (** {3 Printing bitstrings} *)
868 val hexdump_bitstring : out_channel -> bitstring -> unit
869 (** [hexdump_bitstring chan bitstring] prints the bitstring
870 to the output channel in a format similar to the
871 Unix command [hexdump -C]. *)
873 (** {3 Bitstring buffer} *)
877 val create : unit -> t
878 val contents : t -> bitstring
879 val add_bits : t -> string -> int -> unit
880 val add_bit : t -> bool -> unit
881 val add_byte : t -> int -> unit
883 (** Buffers are mainly used by the [BITSTRING] constructor, but
884 may also be useful for end users. They work much like the
885 standard library [Buffer] module. *)
889 These functions let you manipulate individual bits in the
890 bitstring. However they are not particularly efficient and you
891 should generally use the [bitmatch] and [BITSTRING] operators when
892 building and parsing bitstrings.
894 These functions all raise [Invalid_argument "index out of bounds"]
895 if the index is out of range of the bitstring.
898 val set : bitstring -> int -> unit
899 (** [set bits n] sets the [n]th bit in the bitstring to 1. *)
901 val clear : bitstring -> int -> unit
902 (** [clear bits n] sets the [n]th bit in the bitstring to 0. *)
904 val is_set : bitstring -> int -> bool
905 (** [is_set bits n] is true if the [n]th bit is set to 1. *)
907 val is_clear : bitstring -> int -> bool
908 (** [is_clear bits n] is true if the [n]th bit is set to 0. *)
910 val put : bitstring -> int -> int -> unit
911 (** [put bits n v] sets the [n]th bit in the bitstring to 1
912 if [v] is not zero, or to 0 if [v] is zero. *)
914 val get : bitstring -> int -> int
915 (** [get bits n] returns the [n]th bit (returns non-zero or 0). *)
917 (** {3 Miscellaneous} *)
920 (** The package name, always ["ocaml-bitstring"] *)
923 (** The package version as a string. *)
926 (** Set this variable to true to enable extended debugging.
927 This only works if debugging was also enabled in the
928 [pa_bitstring.ml] file at compile time, otherwise it
933 (* Private functions, called from generated code. Do not use
934 * these directly - they are not safe.
937 (* 'extract' functions are used in bitmatch statements. *)
939 val extract_bit : string -> int -> int -> int -> bool
941 val extract_char_unsigned : string -> int -> int -> int -> int
943 val extract_int_be_unsigned : string -> int -> int -> int -> int
945 val extract_int_le_unsigned : string -> int -> int -> int -> int
947 val extract_int_ne_unsigned : string -> int -> int -> int -> int
949 val extract_int_ee_unsigned : endian -> string -> int -> int -> int -> int
951 val extract_int32_be_unsigned : string -> int -> int -> int -> int32
953 val extract_int32_le_unsigned : string -> int -> int -> int -> int32
955 val extract_int32_ne_unsigned : string -> int -> int -> int -> int32
957 val extract_int32_ee_unsigned : endian -> string -> int -> int -> int -> int32
959 val extract_int64_be_unsigned : string -> int -> int -> int -> int64
961 val extract_int64_le_unsigned : string -> int -> int -> int -> int64
963 val extract_int64_ne_unsigned : string -> int -> int -> int -> int64
965 val extract_int64_ee_unsigned : endian -> string -> int -> int -> int -> int64
967 external extract_fastpath_int16_be_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_be_unsigned" "noalloc"
969 external extract_fastpath_int16_le_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_le_unsigned" "noalloc"
971 external extract_fastpath_int16_ne_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_ne_unsigned" "noalloc"
973 external extract_fastpath_int16_be_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_be_signed" "noalloc"
975 external extract_fastpath_int16_le_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_le_signed" "noalloc"
977 external extract_fastpath_int16_ne_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int16_ne_signed" "noalloc"
980 external extract_fastpath_int24_be_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_be_unsigned" "noalloc"
982 external extract_fastpath_int24_le_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_le_unsigned" "noalloc"
984 external extract_fastpath_int24_ne_unsigned : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_ne_unsigned" "noalloc"
986 external extract_fastpath_int24_be_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_be_signed" "noalloc"
988 external extract_fastpath_int24_le_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_le_signed" "noalloc"
990 external extract_fastpath_int24_ne_signed : string -> int -> int = "ocaml_bitstring_extract_fastpath_int24_ne_signed" "noalloc"
993 external extract_fastpath_int32_be_unsigned : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_be_unsigned" "noalloc"
995 external extract_fastpath_int32_le_unsigned : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_le_unsigned" "noalloc"
997 external extract_fastpath_int32_ne_unsigned : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_ne_unsigned" "noalloc"
999 external extract_fastpath_int32_be_signed : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_be_signed" "noalloc"
1001 external extract_fastpath_int32_le_signed : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_le_signed" "noalloc"
1003 external extract_fastpath_int32_ne_signed : string -> int -> int32 -> int32 = "ocaml_bitstring_extract_fastpath_int32_ne_signed" "noalloc"
1006 external extract_fastpath_int40_be_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_be_unsigned" "noalloc"
1008 external extract_fastpath_int40_le_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_le_unsigned" "noalloc"
1010 external extract_fastpath_int40_ne_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_ne_unsigned" "noalloc"
1012 external extract_fastpath_int40_be_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_be_signed" "noalloc"
1014 external extract_fastpath_int40_le_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_le_signed" "noalloc"
1016 external extract_fastpath_int40_ne_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int40_ne_signed" "noalloc"
1018 external extract_fastpath_int48_be_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_be_unsigned" "noalloc"
1020 external extract_fastpath_int48_le_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_le_unsigned" "noalloc"
1022 external extract_fastpath_int48_ne_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_ne_unsigned" "noalloc"
1024 external extract_fastpath_int48_be_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_be_signed" "noalloc"
1026 external extract_fastpath_int48_le_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_le_signed" "noalloc"
1028 external extract_fastpath_int48_ne_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int48_ne_signed" "noalloc"
1030 external extract_fastpath_int56_be_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_be_unsigned" "noalloc"
1032 external extract_fastpath_int56_le_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_le_unsigned" "noalloc"
1034 external extract_fastpath_int56_ne_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_ne_unsigned" "noalloc"
1036 external extract_fastpath_int56_be_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_be_signed" "noalloc"
1038 external extract_fastpath_int56_le_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_le_signed" "noalloc"
1040 external extract_fastpath_int56_ne_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int56_ne_signed" "noalloc"
1043 external extract_fastpath_int64_be_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_be_unsigned" "noalloc"
1045 external extract_fastpath_int64_le_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_le_unsigned" "noalloc"
1047 external extract_fastpath_int64_ne_unsigned : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_ne_unsigned" "noalloc"
1049 external extract_fastpath_int64_be_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_be_signed" "noalloc"
1051 external extract_fastpath_int64_le_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_le_signed" "noalloc"
1053 external extract_fastpath_int64_ne_signed : string -> int -> int64 -> int64 = "ocaml_bitstring_extract_fastpath_int64_ne_signed" "noalloc"
1055 (* 'construct' functions are used in BITSTRING constructors. *)
1056 val construct_bit : Buffer.t -> bool -> int -> exn -> unit
1058 val construct_char_unsigned : Buffer.t -> int -> int -> exn -> unit
1060 val construct_int_be_unsigned : Buffer.t -> int -> int -> exn -> unit
1062 val construct_int_le_unsigned : Buffer.t -> int -> int -> exn -> unit
1064 val construct_int_ne_unsigned : Buffer.t -> int -> int -> exn -> unit
1066 val construct_int_ee_unsigned : endian -> Buffer.t -> int -> int -> exn -> unit
1068 val construct_int32_be_unsigned : Buffer.t -> int32 -> int -> exn -> unit
1070 val construct_int32_le_unsigned : Buffer.t -> int32 -> int -> exn -> unit
1072 val construct_int32_ne_unsigned : Buffer.t -> int32 -> int -> exn -> unit
1074 val construct_int32_ee_unsigned : endian -> Buffer.t -> int32 -> int -> exn -> unit
1076 val construct_int64_be_unsigned : Buffer.t -> int64 -> int -> exn -> unit
1078 val construct_int64_le_unsigned : Buffer.t -> int64 -> int -> exn -> unit
1080 val construct_int64_ne_unsigned : Buffer.t -> int64 -> int -> exn -> unit
1082 val construct_int64_ee_unsigned : endian -> Buffer.t -> int64 -> int -> exn -> unit
1084 val construct_string : Buffer.t -> string -> unit
1086 val construct_bitstring : Buffer.t -> bitstring -> unit